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Serial port mouse

 
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It is possible to attach a serial mouse to the RS232 port.

If a mouse is connected to a Serial Port, the mouse cursor moves jerkily

The problem is the Serial Port HW on the PXA27x. You can only get an interrupt if the Serial FIFO gets to a defined fill level or if no chars are received for a 4 char time period. Now the fill level is set to 32 bytes by default (this means only every 10 mouse positions I get a stream with 10 positions simultaneously...). And if the Char Timeout is too big, I get 2 mouse positions practically back to back. The solution to solve this problem is to set the fill level interrupt to 1 char instead of 32. You can do that by adding the Registry settings:

[HKEY_LOCAL_MACHINE\Drivers\BuiltIn\Serial1]
"WaterMarker"=dword:1

You must Save Registry and reboot.

NOTE: if you use the serial port for something else, do not leave the WaterMarker at 1. This would be very inefficient for normal use.